As well as extracting the useful metals and recycling other materials, not putting your phone, computer or MP3 player in landfill means hazardous materials can be disposed of in a safe manner.
To recycle your phone, visit mobilemuster - the offical programme of the Australian mobile phone industry. You can mail them your handset, or check for a local drop off point.
Many local councils collect E-waste - check with them if you want to ensure the dozens of metals in your computer - not to mention other components - get used again. Visit the Australian Local Government Association for a link.
If they don't provide a service, visit Clean Up Australia or the Total Environment Sector to see what the options are in your area. Many places are simply interested in taking old computers off your hands for resale or refurbishment. Computer users in developing countries are often keen on upgrading their computers with CPUs that Australians may find outdated.
Victorian residents can use the Byteback scheme to get rid of their old computers, but government efforts to take on E-waste in other states are currently limited.